With increasing awareness about the environment and in view of depleted oil sources in the future, there has been a need for reduction of fuel consumption in automobiles, motorcycles, etc. Also, secondary batteries such as a lithium ion battery have been making remarkable progresses. Attempts to use electric power as driving power in electric automobiles, hybrid automobiles, etc., have been vigorously made.
For example, Patent Literature 1 discloses a sport type electric motorcycle incorporating an electric motor of a large size and a high output. In this electric motorcycle, a driving unit including an electric motor and a driving power transmission device is placed in a location where an engine and a transmission are conventionally placed, and a speed of rotation of a motor shaft is reduced by gears to increase torque, and then the rotation is transmitted to a rear wheel via a chain.